Food packaging container

Abstract

A food packaging container having a flanged container body of a laminate sheet which comprises a layer of aluminum foil and at leasat one thermoplastic resin layer joined to one surface of the foil layer. The container body is prepared by deep-drawing the laminate sheet with the resin layer inside. The aluminum foil is 40-200 μm in thickness, 9.0-25.0 kgf/mm 2 in tensile strength, 2.5-9.5 kgf/mm 2 in proof stress, 10 to 40% in elongation and up to 7% in earing ratio. The resin layer comprises a thermoplastic resin 100-500 μm in thicknes, 0.92-1.08 in the ratio of modulus of elasticity in tension in the machine directon (MD) to that in the transverse direction (TD), 0.60-1.40 in the MD/TD ratio of elongation and 0.40-1.60 in the MD/TD ratio of breaking strength.

What is claimed is: 
     
       1. A food packaging container having a flanged container body of a laminate sheet comprising a layer of aluminum foil and at least one thermoplastic resin layer joined to one surface of the foil layer, the container body being prepared by deep-drawing the laminate sheet with the resin layer inside, the container being characterized in that the aluminum foil layer of the laminate sheet comprises an aluminum foil 40-200 μm in thickness, 9.0-25.0 kgf/mm 2  in tensile strength, 2.5-9.5 kgf/mm 2  in proof stress, 10 to 40% in elongation and up to 7% in earing ratio, the thermoplastic resin layer of the sheet comprising a thermoplastic resin 100-500 μm in thickness, 0.92-1.08 in the ratio of modulus of elasticity in tension in the machine direction (MD) to that in the transverse direction (TD), 0.60-1.40 in the MD/TD ratio of elongation and 0.40-1.60 in the MD/TD ratio of breaking strength. 
     
     
       2. A container as defined in claim 1 wherein the laminate sheet is deep-drawn at a drawing ratio (depth of the container body H/opening diameter of the container body W) of at least 40%. 
     
     
       3. A container as defined in claim 1 wherein the resin layer positioned on the surface side of the container body and to be joined to a heat-sealing material layer of a lid is separably joined to the layer on the rear side of the resin layer, and the flange is formed in the surface-side resin layer with an annular incision positioned in the vicinity of the opening-defining inner periphery of the container body and extending along the entire circumference of the flange. 
     
     
       4. A container as defined in claim 3 wherein the thermoplastic resin layer of the laminate sheet comprises at least two resin layers, and the resin layer on the surface side to be joined to the heat-sealing material layer of the lid is separably joined to the resin layer on the rear side thereof with a bond strength of 500-1500 g/15 mm width. 
     
     
       5. A container as defined in claim 3 wherein the thermoplastic resin layer of the laminate sheet is in the form of a single resin layer, and the resin layer is separably joined to the aluminum foil layer on the rear side thereof by a joint layer with a bond strength of 500 to 1500 g/15 mm width. 
     
     
       6. A container as defined in claim 4 wherein the thermoplastic resin layer of the laminate sheet comprises unstretched co-extruded thermoplastic resins in the form of at least two resin layers. 
     
     
       7. A container as defined in claim 6 wherein the surface-side resin layer of the unstretched co-extruded thermoplastic resin layer is made of high-density polyethylene, and the resin layer separably joined to the rear side thereof is made of one of polypropylene and a mixture of polypropylene and polyethylene. 
     
     
       8. A container as defined in claim 4 wherein the resin layer on the surface side of the thermoplastic resin layer of the laminate sheet is separably joined to the resin layer on the rear side thereof with an adhesive layer. 
     
     
       9. A container as defined in claim 4 wherein the aluminum foil layer is joined to the thermoplastic resin layer with at least one adhesive selected from the group consisting of urethane adhesive, polyester adhesive, and monoolefin-unsaturated carboxylic acid copolymer resins or metal salts thereof. 
     
     
       10. A container as defined in claim 3 wherein the annular incision is formed in the surface-side resin layer of the flange simultaneously when the heat-sealing material layer of the lid is fused to the surface-side resin layer by a heat-pressing member of a heat-sealing device having an annular projection projecting downward from the inner periphery of the lower surface of the member. 
     
     
       11. A container as defined in claim 3 wherein the flange of the container body has a bent edge at its outer end and is formed in the surface-side resin layer with an annular outer incision positioned approximately at the bent edge portion and extending along the entire circumference of the flange, and the heat-sealing material layer of the lid is fused to the surface-side resin layer over the portion thereof between the outer incision and the inner incision positioned toward the opening-defining inner periphery of the container body. 
     
     
       12. A container as defined in claim 11 wherein the annular outer incision is formed in the surface-side resin layer of the flange simultaneously when the heat-sealing material layer of the lid is fused to the surface-side resin layer by a heat-pressing member of a heat-sealing device having an annular projection projecting downward from the outer periphery of the lower surface of the member. 
     
     
       13. A container as defined in claim 11 wherein the annular outer incision is provided in the vicinity of the bent edge of the flange, and a fusion preventing layer is provided on the surface of one of the resin layer of the flange and the heat-sealing material layer of the lid and positioned between the outer incision and the bent ege. 
     
     
       14. A container as defined in claim 1 wherein a synthetic resin protective covering layer is provided over the outer surface of the aluminum foil layer. 
     
     
       15. A container as defined in claim 14 wherein a synthetic resin ground layer containing a zirconium compound is formed on one surface of the aluminum foil layer, and the protective covering layer is joined to the ground layer. 
     
     
       16. A container as defined in claim 14 wherein a synthetic resin ground layer containing a chromium compound is formed on one surface of the aluminum foil layer, and the protective covering layer is joined to the ground layer. 
     
     
       17. A container as defined in claim 14 wherein the protective covering layer provided over the outer surface of the aluminum foil layer is made of a synthetic resin non-fusible to a heat-sealing material layer of a lid, and the flange of the container body is formed at its outer end with a curled edge having the thermoplastic resin layer positioned inside and the non-fusible protective covering layer positioned outside, the flange being formed in the resin layer on the surface side thereof with inner and outer two annular incisions positioned approximately at the opening-defining inner peripheral portion of the container body and at the base end of the curled edge respectively and extending generally along the entire circumference of the flange. 
     
     
       18. A container as defined in claim 1, wherein said laminate sheet comprises said aluminum foil layer and at least two thermoplastic resin layers, and the resin layer on the surface side to be joined to a heat-sealing material layer of a lid is separably joined to said resin layer of the rear side thereof with a bond strength of 500-1500 g/15 mm width, and the flange is formed in the surface-side resin layer with an annular incision positioned in the vicinity of the opening-defining inner periphery of the container body and extending along the entire circumference of the flange, and the aluminum foil layer is joined to the at least two thermoplastic resin layers with at least one adhesive selected from the group consisting of urethane adhesive, polyester adhesive, and monoolefin-unsaturated carboxylic acid copolymer resins or meal salts thereof. 
     
     
       19. A container as defined in claim 18, wherein the at least two thermoplastic resin layers joined to the aluminum foil layer of the laminate sheet comprises unstretched co-extruded thermoplastic resin in the form of at least two resin layers. 
     
     
       20. A container as defined in claim 19, wherein the surface-side resin layer of the unstretched co-extruded thermoplastic resin layer is made of a high-density polyethylene, and the resin layer separably joined to the rear side thereof is made of one of polypropylene and a mixture of polypropylene and polyethylene. 
     
     
       21. A container as defined in claim 1, wherein the flange of the container body has a bent edge at its outer end and is formed in the surface-side resin layer with an annular outer incision positioned approximately at the bent edge portion and extending along the entire circumference of the flange, and a heat-sealing material layer of a lid is fused to the surface-side resin layer over the portion thereof between the outer incision and the inner incision positioned toward the opening-defining inner periphery of the container body. 
     
     
       22. A container as defined in claim 1, wherein a synthetic resin protective covering layer is provided over the outer surface of the aluminum foil layer. 
     
     
       23. A container as defined in claim 22, wherein a synthetic resin ground layer containing a zirconium compound is formed on one surface of the aluminum layer, and the protective covering layer is joined to the ground layer. 
     
     
       24. A container as defined in claim 22, wherein a synthetic resin ground layer containing a chromium compound is formed on one surface of the aluminum foil layer, and the protective covering layer is joined to the ground layer. 
     
     
       25. A container as defined in claim 22, wherein the protective covering layer provided over the outer surface of the aluminum foil layer is made of a synthetic resin non-fusible to a heat-sealing material layer of a lid, and the flange of the container body is formed at it outer end with a curled edge having the thermoplastic resin layer positioned inside and the non-fusible protective covering layer positioned outside, the flange being formed in the resin layer on the surface side thereof with inner and outer annular incisions positioned approximately at the opening-defining inner peripheral portion of the container body and at the base end of the curled edge, respectively, and extending generally along the entire circumference of the flange.